Initial attempt at defining an equ operator

As per PPC0030.

Currently only defines the stringy version, not the numerical version.

TODO: Currently lacks any attempt at documentation or perldelta.

TODO: Also lacks any consideration on how an `equ` operator would
  interact with `use overload`. Further thought is required here.

fixup with magic

MANIFEST

@@ -6315,6 +6315,7 @@ t/op/dor.t				See if defined-or (//) works
 t/op/dump.t				See if dump works.
 t/op/each.t				See if hash iterators work
 t/op/each_array.t			See if array iterators work
+t/op/equ.t				See if the equ operator works
 t/op/eval.t				See if eval operator works
 t/op/evalbytes.t			See if evalbytes operator works
 t/op/exec.t				See if exec, system and qx work

gv.c

@@ -614,7 +614,7 @@ S_maybe_add_coresub(pTHX_ HV * const stash, GV *gv,
     case KEY_catch   : case KEY_class   :
     case KEY_continue: case KEY_cmp     : case KEY_defer :
     case KEY_do      : case KEY_dump   : case KEY_else  : case KEY_elsif  :
-    case KEY_eq     : case KEY_eval  : case KEY_field  :
+    case KEY_eq      : case KEY_equ     : case KEY_eval  : case KEY_field  :
     case KEY_finally:
     case KEY_for     : case KEY_foreach: case KEY_format: case KEY_ge     :
     case KEY_goto   : case KEY_grep  : case KEY_gt     :